Electronic components such as semiconductor components, and functional groups such as to analog circuits and wireless circuits have been mounted on a printed circuit board. In case that a printed circuit board is electromagnetically shielded, either the electronic component or the functional group to be electromagnetically shielded is covered by a case made of metal, and the metal case is electrically connected to a ground terminal of the printed circuit board by way of solder. Instead of the metal case, there is a case that a cover made of resin and having an inner plated metal layer may be employed. Furthermore, instead of the metal case and the resin case, there is another case that an electromagnetic wave absorbing sheet capable of weakening electromagnetic waves may be employed.
However, in the conventional electromagnetic shielding methods by way of the metal case and the resin cover, it is necessary to ensure a large area where a metal case component or a resin cover component is in contact to the printed circuit board. As a result, the large contact area may largely impede mounting of the electronic components in high density. Also it is required to avoid that an electronic component and a semiconductor component are in contact to the metal case or the resin cover. For this reason, when the electromagnetic shield is carried out, the height of a device becomes high.
Further, in the method of using the electromagnetic wave absorbing sheet, the electromagnetic shielding effect is small. In addition, this method cannot solve electromagnetic interference among the respective electronic components, but also cannot reinforce the printed circuit board.
In conjunction with the above description, an electromagnetic shielding method is disclosed in Japanese Laid Open Utility Model Application (JU-A-Heisei 2-45699). In this conventional example, insulating films are formed on surfaces of a circuit board on which electronic components are mounted. Subsequently, an electric conductive shield films are formed on the insulating films. Thereafter, the electric conductive shield films are connected to an earth line formed on the electronic circuit board.
Also, another electromagnetic shielding method is disclosed in Japanese Laid Open patent Application (JP-A-Heisei 4-58596). In this conventional example, electronic circuit components on the printed circuit board is partitioned by electric conductors which are connected to a ground portion of the printed circuit board to prevent mutual electromagnetic inference between the electronic circuit components. Subsequently, the printed circuit board and the entire of electronic circuit components mounted on this printed-wiring board are covered by an insulating sealing resin or an insulating thin-film seal, which can be easily peeled later. Subsequently, a portion of the electric conductor is exposed from the sealing resin or the thin-film seal. Next, a metal plating layer or an electric conductive paint layer is coated on the sealing resin or the thin-film seal in such a manner that the metal plating layer or the electric conductive paint layer is connectable to the electric conductor.
Also, a shielding device is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 4-72698). In this conventional example, a portion of a printed circuit board where electronic components are mounted is covered by a bag made of thermal shrinkage resin. An electric conductive film has been formed on the outer surface of this bag. A ground pattern formed on an exposed portion of the printed circuit board is connected to the electric conductive film by a lead wire.
Also, a method of manufacturing a high frequency module is disclosed in Japanese Laid Open Patent Application (JP-P2000-223647A). In the high frequency module manufacturing method of this conventional example, a printed circuit board is provided on which electronic components have been mounted and a ground terminal having a predetermined height has been formed. One surface side of the printed circuit board on which electronic components have been mounted is covered by a stacked sheet in which an insulating resin film and an electric conductive film having the shield effect are laminated. The printed circuit board is heated so as to soften the insulating resin film, so that the ground terminal and the electric conductive film are electrically connected.
Also, a memory module is disclosed in Japanese Laid Open Patent Application (JP-P2000-251463A). In the memory module of this conventional example, a memory chip is mounted on a portion of one surface of a printed circuit board. This portion of one surface of the printed circuit board is covered by a shield sheet formed by stacking an adhesive sheet and an aluminum sheet. Thus, the shield sheet is adhered on the upper surface of the memory chip and the upper surface of the printed circuit board so that the semiconductor memory chip is electromagnetically shielded and is fixed on the printed circuit board. As a result, electromagnetic noise radiated from the memory chip is shield by the aluminum sheet. Also, since the memory chip is fixed by the adhesive sheet, the occurrence of a connection failure caused through vibration may also be suppressed. Furthermore, the aluminum sheet functions as a heat radiating plate, so that the heat radiation of the memory module may be improved.